Disble UART on Jetson Nano Prevents boot on some SoMs

[kevin89]

We have a custom carrier board where we have a connection for a external USB UART. An issue we just ran into is that on some Jetson SoMs EMMC they get stuck if UART is not present. This is odd because we have 50+ SoMs that do not show this behavior and we’re seeing it only on SoMs that were manufactured most recently.

I found a forum post that described a HW fix by setting the RX UART pin to high or low with a 10k ohm shunt. We did this and it is set high 1.8V. This fixes the issue but we have quite a few of these boards made.

Do you think disabling UART check on these boards would fix the issue? If so do you have a link on how to do that?

Edit: Link to other forum post.

Jetson Nano won’t boot without UART to USB attached to serial console

I’m having the same exact issue as this person: https://forums.developer.nvidia.com/t/jetson-nano-wont-boot-without-uart-to-usb-attached-to-serial-console/176066 I have a custom motherboard for the TX2, pin compatible with the other Nano and Xavier. The SoM is not booting properly without UART to USB attatched so the console can print out the boot log. I’m trying to log in remotely via SSH through a usb ethernet adaptor connected to USB 2.0 of the Jetson. The usb ethernet adaptor is only recogn…

Edit 2: I know there are quite a few links to disabling this in older posts relating to this topic but all those links area dead.

[KevinFFF]

Hi kevin89,

What’s the Jetpack version in use for Jetson Nano?

@kevin89

his is odd because we have 50+ SoMs that do not show this behavior and we’re seeing it only on SoMs that were manufactured most recently.

Have you confirmed that they are the exact same module?
You can run cat /etc/nv_boot_control.conf to check.

@kevin89

An issue we just ran into is that on some Jetson SoMs EMMC they get stuck if UART is not present.

What do you mean that “UART is not present”?
Which UART interface do you mean or you mean a USB-UART cable?
Please also share the full serial console log when you hit the stuck issue.

[Trumany]

Please read the Design Guide doc to make sure if the UART pins are strapping pins and also refer to below info in DG.

[kevin89]

Thank you for the feedback and I saw that but we don’t use a level shifter. Our connection is straight to the Jetson Nano UART2_RXD.

[kevin89]

We are on Jetpack 4.5.1 (latest we can be on for the moment) since we have Jetson Nano, not Orin Nano.

When you say the same module, are you suggesting that they are the SD card version? There are only two Nvidia Jetson Modules that I’m aware of. We ordered all of our units directly from Arrow and they are the 16GB EMMC version. The output of that command is as follows.

Blockquote
ansible@XXXXX:~$ cat /etc/nv_boot_control.conf
TNSPEC 3448-300—1-0-jetson-nano-qspi-sd-mmcblk0p1
COMPATIBLE_SPEC 3448-300—1–jetson-nano-devkit-mmcblk0p1
TEGRA_CHIPID 0x21
TEGRA_OTA_BOOT_DEVICE /dev/mtdblock0
TEGRA_OTA_GPT_DEVICE /dev/mtdblock0

The product model number on the offending SoMs is the same as the SoMs that do not exhibit this issue.

Our implementation utilizes a USB UART interface. There isn’t anything I can share because the unit boots when you have it connected but won’t when disconnected. Due to the design we don’t have a display output on this unit. When we solder a pullup to UART2_RXD it also boots.

[Trumany]

@kevin89

Thank you for the feedback and I saw that but we don’t use a level shifter. Our connection is straight to the Jetson Nano UART2_RXD.

It is same requirement to UART2_RXD without level shift to keep the input from floating.

[kevin89]

Well, that is unfortunate but I appreciate you making the clarification. At least the rework on these boards is straight forward. Jetson Nano is a mostly EOL product but would have been a good addition to include that detail in the design guide.